Internet DRAFT - draft-yang-masque-dgram-retrans
draft-yang-masque-dgram-retrans
MASQUE F. Yang
Internet-Draft Y. Liu
Intended status: Experimental Y. Ma
Expires: 14 September 2023 Alibaba Inc.
13 March 2023
A Configurable Retransmission Extension for HTTP/3 Datagrams
draft-yang-masque-dgram-retrans-01
Abstract
When using HTTP/3 Datagrams for traffic tunneling, it is desirable to
retransmit HTTP/3 Datagrams in some scenarios where the
retransmission is beneficial for the tunneled end-to-end connection.
This document defines an extension to the HTTP Datagrams and the
Capsule Protocol, which allows HTTP/3 Datagrams to be retransmitted
according to the configuration of the HTTP/3 Datagram flow.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Multiplexed
Application Substrate over QUIC Encryption Working Group mailing list
(masque@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/masque/.
Source for this draft and an issue tracker can be found at
https://github.com/yangfurong/draft-yang-masque-retx-dgrams.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 September 2023.
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Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Negotiating The Extension Between Peers . . . . . . . . . . . 4
4. Signaling HTTP/3 Datagram Retransmission Limit . . . . . . . 4
5. Updating HTTP/3 Datagram Retransmission Limit . . . . . . . . 5
6. Handling Lost HTTP/3 Datagrams . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
HTTP Datagrams and the Capsule Protocol [HTTP-DATAGRAM] defines how
HTTP Datagrams can be sent either unreliably using the QUIC DATAGRAM
extension [QUIC-DATAGRAM] or reliably using the Capsule Protocol that
encapsulates HTTP Datagrams into HTTP/2 [RFC7540] streams, HTTP/3
[RFC9114] streams or HTTP/1.x connections. The two modes, "reliable
mode" and "unreliable mode", all have their pros and cons.
This document takes the scenario where HTTP Datagrams are leveraged
to tunnel QUIC [QUIC] connections from a QUIC client and a target
QUIC server via an HTTP UDP proxy [CONNECT-UDP] as a reference.
However, the problems discussed below are not restricted to the
reference scenario. Instead, the problems are general in other
scenarios using HTTP Datagrams for traffic tunneling, e.g.
[CONNECT-IP].
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In the reference scenario, the reliable mode is usually worse than
the unreliable mode in terms of the transport performance of the end-
to-end QUIC connection (i.e. the connection tunneled by the proxy).
The culprit is that the stream-based Capsule Protocol can stall the
end-to-end QUIC connection due to head-of-line blocking, which can
inflate the RTT estimation of the end-to-end connection, make the
connection perceive bursty losses, and hinder different streams of
the connection from independent delivery. However, the reliable mode
also has advantages sometimes. If the network path between the
client and the UDP proxy is lossy and the end-to-end delay is a few
times higher than the delay of the tunnel, the reliable mode can
quickly recover the lost packets in the tunnel, hide the losses from
the end-to-end connection, and avoid the reduction of the
connection's congestion window. Some of the above behaviors were
observed by a study [MASQUE-EVALUATION].
This document defines an extension to the Capsule Protocol
[HTTP-DATAGRAM], which allows HTTP/3 Datagrams to be retransmitted
according to the configuration of the HTTP/3 Datagram flow. In
Section 4, a new Capsule Type is added to configure peers'
retransmission limit of HTTP/3 Datagrams. Having such a signaling
mechanism instead of just locally configuring the retransmission
capability at endpoints (i.e. the client and the proxy) is necessary
for enforcing retransmission policies in both upstream and downstream
directions. As the proxy does not know the end-to-end connection's
preference for retransmission, the client needs to inform the proxy
what is the retransmission preference. Depending on the
retransmission limit of HTTP/3 Datagrams, the handling of lost HTTP/3
Datagrams is discussed in Section 6.
This extension brings the benefits of the reliable mode to the
unreliable mode. It is beneficial for traffic tunneling scenarios
where the last-mile link could be very lossy (e.g. Apple's iCloud
Private Relay scenario [PR] where the last-mile link is usually
wireless).
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the notation from [QUIC] for the format of the new
capsule definition. Where fields are encoded using the variable-
length integer, they need not be encoded on the minimum number of
bytes.
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In this document, the term "UDP proxy" aligns with the definition in
[CONNECT-UDP], and the term "intermediary" refers to an HTTP
intermediary as defined in Section 3.7 of [RFC9110].
The term "HTTP/3 Datagram flow" describes the HTTP/3 Datagrams
associated with the same HTTP request, .e.g a Connect-UDP request
[CONNECT-UDP] or a Connect-IP request [CONNECT-IP].
3. Negotiating The Extension Between Peers
Peers indicate support for this extension by including the boolean-
valued Item Structured Field "DG-Retrans: ?1" in the HTTP Request and
Response headers (See Section 3.3.6 of [RFC8941] for information
about the boolean format.). Peers MUST NOT use any following
mechanisms described by this extension unless the support is
explicitly expressed.
4. Signaling HTTP/3 Datagram Retransmission Limit
This document defines a new Capsule Type SET_H3_DGRAM_RETX_LIMIT to
communicate how many times an HTTP/3 Datagram can be retransmitted at
most between peers. Note, the retransmission limit takes effect
within the scope of an HTTP/3 Datagram flow.
The format of the SET_H3_DGRAM_RETX_LIMIT capsule is shown in
Figure 1. It has the following fields:
Context ID: It is the Context ID defined in [CONNECT-UDP] or
[CONNECT-IP]. It describes the effect scope of the capsule. It is
optional. If the Capsule Type is 0xbb (tentative), the capsule has
no Context ID field, and the retransmission limit applies to all
contexts.
Retransmission Limit: It is the maximum retransmission number of an
HTTP/3 Datagram.
SET_H3_DGRAM_RETX_LIMIT {
Capsule Type (i) = 0xba..0xbb,
Capsule Length (i),
[Context ID (i)],
Retransmission Limit (i),
}
Figure 1: SET_H3_DGRAM_RETX_LIMIT Format
When a peer that recognizes SET_H3_DGRAM_RETX_LIMIT capsules receives
a SET_H3_DGRAM_RETX_LIMIT capsule, if it is using HTTP/3 Datagrams,
it MUST start to retransmit lost HTTP/3 Datagrams until they are
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acknowledged or their retransmission limit specified in the capsule
is reached. If the peer is an intermediary, it SHOULD NOT forward
the capsule to the next hop, as the aim of retransmissions is to
recover the lost packets at the probably lossy last-mile link between
the client and the first hop proxy. If an intermediary does not
recognize SET_H3_DGRAM_RETX_LIMIT capsules, it SHOULD forward the
capsules without any modification for the future extensibility as
suggested by [HTTP-DATAGRAM].
Finding the best way to set the limit of retransmission is out of
this document's scope. Nonetheless, a possible way to calculate the
retransmission limit is as follows. Considering the reference
scenario of this document (shown in Figure 2), the client can set its
local retransmission limit to floor(RTT2 / RTT1) and use the
SET_H3_DGRAM_RETX_LIMIT capsule to set the proxy's retransmission
limit to floor(RTT2 / RTT1). As the loss detection algorithm takes
at least one RTT to detect a packet loss, this setting intends to
only allow a lost packet to be retransmitted by the tunnel before it
is retransmitted by the end-to-end QUIC connection. Note, the client
can subtract RTT1 from the RTT of the end-to-end QUIC connection to
get RTT2.
┌───────────────┐ ┌─────────┐ ┌───────────┐
│ QUIC Client │ RTT1 │UDP Proxy│ RTT2 │QUIC Server│
├───────────────┼──────────────┤ ├────────────┤ │
│ MASQUE Client │ │ │ │ │
└───────────────┘ └─────────┘ └───────────┘
Figure 2: The reference scenario
5. Updating HTTP/3 Datagram Retransmission Limit
A peer can just send a new SET_H3_DGRAM_RETX_LIMIT capsule to update
the retransmission limit of its peer if necessary. Note, the new
limit will overwrite the old limit specified by a previous
SET_H3_DGRAM_RETX_LIMIT capsule.
6. Handling Lost HTTP/3 Datagrams
HTTP/3 Datagrams are encoded in QUIC DATAGRAM frames. As described
in [QUIC-DATAGRAM], QUIC MAY notify the sender upon a QUIC DATAGRAM
frame is acknowledged or declared lost by the loss detection
algorithm. This extension relies on the notifications of the
acknowledgement and loss of QUIC DATAGRAM frames to handle the
retransmission of lost HTTP/3 Datagrams.
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A reference way of implementation is as follows. First, when the
HTTP/3 Datagram layer calls the unreliable sending API of QUIC to
send an HTTP/3 Datagram, it gets a connection-level unique ID
(DATAGRAM_ID) from QUIC that corresponds to the underlying QUIC
DATAGRAM frame. Then, if the retransmission limit is larger than
zero, the HTTP/3 Datagram layer generates a record {id = DATAGRAM_ID,
retx_times = 0} for the HTTP/3 Datagram. Afterwards, whether the
HTTP/3 Datagram is acknowledged or declared lost, the HTTP/3 Datagram
layer will get a corresponding notification. For the acknowledgement
notification, the HTTP/3 Datagram layer just deletes the record. For
the loss notification, the HTTP/3 Datagram layer retransmits the
HTTP/3 Datagram and updates the id and retx_times of the record if
the retransmission limit permits, otherwise, the record is deleted.
Note, as QUIC holds the HTTP/3 Datagram as the payload of the QUIC
DATAGRAM frame, the payload can be returned to the HTTP/3 Datagram
layer for retransmission, which saves the HTTP/3 Datagram layer from
buffering HTTP/3 Datagrams for retransmission.
7. Security Considerations
This extension adds no additional considerations to those presented
in [HTTP-DATAGRAM].
8. IANA Considerations
This document adds following entry to the "Hypertext Transfer
Protocol (HTTP) Field Name Registry":
+==============+========+===============+
| Header Field | Status | Reference |
+==============+========+===============+
| DG-Retrans | Exp | This document |
+--------------+--------+---------------+
Table 1: New HTTP Header Field
This document adds following entries to the "HTTP Capsule Types"
registry:
+=========================+============+===============+
| Capsule Type | Value | Specification |
+=========================+============+===============+
| SET_H3_DGRAM_RETX_LIMIT | 0xba, 0xbb | This document |
+-------------------------+------------+---------------+
Table 2: New Capsule Type
9. References
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9.1. Normative References
[CONNECT-IP]
Pauly, T., Schinazi, D., Chernyakhovsky, A., Kühlewind,
M., and M. Westerlund, "IP Proxying Support for HTTP",
Work in Progress, Internet-Draft, draft-ietf-masque-
connect-ip-03, 27 September 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-masque-
connect-ip-03>.
[CONNECT-UDP]
Schinazi, D., "Proxying UDP in HTTP", RFC 9298,
DOI 10.17487/RFC9298, August 2022,
<https://www.rfc-editor.org/rfc/rfc9298>.
[HTTP-DATAGRAM]
Schinazi, D. and L. Pardue, "HTTP Datagrams and the
Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, August
2022, <https://www.rfc-editor.org/rfc/rfc9297>.
[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[QUIC-DATAGRAM]
Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", RFC 9221,
DOI 10.17487/RFC9221, March 2022,
<https://www.rfc-editor.org/rfc/rfc9221>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
9.2. Informative References
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[MASQUE-EVALUATION]
Kühlewind, M., Carlander-Reuterfelt, M., Ihlar, M., and M.
Westerlund, "Evaluation of QUIC-based MASQUE proxying",
Proceedings of the 2021 Workshop on Evolution, Performance
and Interoperability of QUIC, DOI 10.1145/3488660.3493806,
December 2021, <https://doi.org/10.1145/3488660.3493806>.
[PR] Apple Inc., "iCloud Private Relay Overview", 2021.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/rfc/rfc7540>.
[RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
[RFC9114] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/rfc/rfc9114>.
Contributors
TBD.
Acknowledgments
The authors would like to thank Qinghua Wu, Jiaxing Zhang, and Zhenyu
Li for discussions and comments on the design of this draft.
Authors' Addresses
Furong Yang
Alibaba Inc.
Email: yfr256538@alibaba-inc.com
Yanmei Liu
Alibaba Inc.
Email: miaoji.lym@alibaba-inc.com
Yunfei Ma
Alibaba Inc.
Email: yunfei.ma@alibaba-inc.com
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